limit (1/x^2) , x -------> negative infinity
limit[ (x^2 - 2x +1) / (x-1) ] , x ------> positive infinity
limit [square root (2 x ^2 + 4) / (x +5) ], x -------> positive infinity
limit[ (3 x) / square root ( 2 + 4 x ^3)] , x --------> positive infinity